Biomedical Engineering Reference
In-Depth Information
The.sample-to-result.turnaround.can.be.several.weeks.
7
.Hence,.ART.monitoring.tools.
are.urgently.needed.at.the.point.of.care.(POC).to.effectively.decrease.the.turnaround.
time.
Due.to.the.lack.of.resources,.ART.is.often.initiated.in.sub-Saharan.Africa.without.testing.
CD4
+
.cell.count.and.viral.load.
8,9
.This.has.been.a.concern.since.HIV-1.lacks.stringent.proof-
reading.in.RNA.synthesis.and.results.in.mutations.in.the.genome..In.addition,.coinfection.
of.different.HIV-1.subtypes.facilitates.RNA.recombination..Thus,.HIV-1.can.rapidly.pro-
duce.drug-resistant.strains.and.can.render.the.irst-line.drugs.ineficacious..The.second-line.
therapy,.though.available,.can.yield.annual.costs.up.to.$1,037.per.person,.2.4.times.higher.
than.the.irst-line.therapy.
10
.Due.to.discontinuous.logistics.or.drug.toxicity,.ART.is.often.
interrupted,.which.breeds.more.chances.for.drug.resistance.to.develop,.and.thus.leads.to.
treatment. failure.
11
. When. this. scenario. occurs,. although. ART. is. switched. to. second-line.
drugs,.AIDS.patients.most.likely.experience.rapid.disease.progression..Some.studies.have.
shown.that.viral.load.monitoring.is.needed.to.detect.early.virological.failure.
12,13
.However,.
current.commercial.viral.load.assays.(e.g.,.reverse-transcriptase.polymerase.chain.reaction.
(RT-PCR)). and. inexpensive. alternatives. (e.g.,. ExaVir
reverse. transcriptase. assay). are. still.
not.practical.for.resource-limited.settings.
14
.Accordingly,.CD4
+
T.cell.count.is.an.essential.
standard.for.monitoring.ART,.and.it.can.be.safely.used.to.determine.if.the.treatment.regi-
mens.should.be.changed.
15,16
.Thus,.the.remaining.issue.transforms.to.how.to.develop.low-
cost,.portable,.and.rapid.CD4
+
.cell.counting.systems.without.the.need.for.highly.trained.
end.users.at.the.POC.
17-19
To.address.this.global.health.issue,.extensive.efforts.exist.to.simplify.CD4
+
.cell.counting.
technologies,.where.low.cytometry.is.the.“gold.standard.”.However,.the.implementation.
of.simpliied.low.cytometers.is.still.challenging.due.to.high.cytometer.cost.($27,000-$35,000),.
high. cost. per. test. ($5-$20),. limited. throughput. (30-50. samples/day),. and. need. for.
trained. skilfful. operators.. Simpliied. low. cytometers. such. as. EasyCD4,
20
. CyFlow,
21
. and.
Pan-leucogating
22
. have. been. developed,. signiicantly. reducing. the. initial. cost. on. instru-
ment. setup.. In. addition,. manual. assays. such. as. Dynabeads. and. Cytosphere. have. been.
developed.for.de-centralized.laboratories..However,.these.two.methods.are.time-consum-
ing.and.labor-intensive..More.recently,.microluidic-based.CD4
+
.cell.count.technology.has.
moved.rapidly.forward,.from.luorescence.staining.to.lensless.imaging,.to.suit.the.need.for.
POC.diagnosis.
18,23,24
.These.microaluidic.methods.uptake.small.volumes.of.whole.blood.
and.report.CD4
+
.cell.count.within.30.minutes,.showing.the.potential.to.deliver.an.afford-
able.solution.to.scale.up.ART.in.resource-limited.settings.
In. this. chapter,. we. will. irst. present. the. gold. standard. (i.e.,. low. cytometry). and. its.
simpliied. derivatives.. Manual. CD4
+
. cell. counting. methods,. which. were. developed. for.
resource-limited.settings,.will.be.also.reviewed..Most.importantly,.we.will.discuss.the.lat-
est.microluidic.and.imaging.techniques.for.developing.POC.CD4
+
.assays.
6.2 FlowCytometryforCD4
+
CellCountsinResource-LimitedSettings
6.2.1 Gold Standard in Resource-Limited Settings
Traditionally,.CD4
+
.cell.count.is.performed.by.using.a.dual-platform.technology;.a.hema-
tology.analyzer.is.used.to.quantify.the.total.number.of.white.blood.cells,.and.a.low.cytom-
eter. is. used. to. measure. the. percentage. of. CD4
+
. T. lymphocytes.. To. simplify. the. testing.
